1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus for manufacturing a semiconductor device. More particularly, embodiments of the present invention an apparatus for thermally processing a substrate.
2. Description of the Related Art
During semiconductor processing, substrates may be heated to high temperatures so that various chemical and/or physical reactions can take place. Thermal processes are usually used to heat the substrates. A typical thermal process, such as annealing, requires providing a relatively large amount of thermal energy to the substrate in a short amount of time, and thereafter rapidly cooling the wafer to terminate the thermal process. Examples of thermal processes currently in use include Rapid Thermal Processing (RTP) and impulse (spike) annealing. While such processes are widely used, current technology is not ideal. It tends to ramp the temperature of the wafer too slowly and expose the wafer to elevated temperatures for too long. These problems become more severe with increasing wafer sizes, increasing switching speeds, and/or decreasing feature sizes.
In general, these thermal processes heat the substrates under controlled conditions according to a predetermined thermal recipe. These thermal recipes fundamentally consist of a temperature that the semiconductor substrate must be heated to the rate of change of temperature, i.e., the temperature ramp-up and ramp-down rates and the time that the thermal processing system remains at a particular temperature. For example, thermal recipes may require the substrate to be heated from room temperature to distinct temperatures of 1200° C. or more, for processing times at each distinct temperature ranging up to 60 seconds, or more.
Moreover, to meet certain objectives, such as minimal inter-diffusion of materials between different regions of a semiconductor substrate, the amount of time that each semiconductor substrate is subjected to high temperatures must be restricted. To accomplish this, the temperature ramp rates, both up and down, are preferably high. In other words, it is desirable to be able to adjust the temperature of the substrate from a low to a high temperature, or visa versa, in as short a time as possible.
The requirement for high temperature ramp rates led to the development of Rapid Thermal Processing (RTP), where typical temperature ramp-up rates range from 200 to 400° C./s, as compared to 5-15° C./minute for conventional furnaces. Typical ramp-down rates are in the range of 80-150° C./s. A drawback of RTP is that it heats the entire wafer even though the IC devices reside only in the top few microns of the silicon wafer. This limits how fast one can heat up and cool down the wafer. Moreover, once the entire wafer is at an elevated temperature, heat can only dissipate into the surrounding space or structures. As a result, today's state of the art RTP systems struggle to achieve a 400° C./s ramp-up rate and a 150° C./s ramp-down rate.
To resolve some of the problems raised in conventional RTP type processes various scanning laser anneal techniques have been used to anneal the surface(s) of the substrate. In general, these techniques deliver a constant energy flux to a small region on the surface of the substrate while the substrate is translated, or scanned, relative to the energy delivered to the small region. Due to the stringent uniformity requirements and the complexity of minimizing the overlap of scanned regions across the substrate surface these types of processes are not effective for thermal processing contact level devices formed on the surface of the substrate.
Pulsed laser anneal techniques, generally project a pulsed electromagnetic energy at one small region on the substrate, and then move the substrate relative to the energy source and expose other small region to a pulsed electromagnetic energy. The pulsed laser anneal techniques minimizes overlap between processing regions on the substrate, therefore improving thermal annealing uniformity. However, the energy sources used in the pulsed laser anneal techniques must be able to deliver a relative large amount of energy at a relatively short time period, therefore, are expensive.
In view of the above, there is a need for an apparatus for annealing a semiconductor substrate with increased uniformity and reduced cost for ownership.